Method of growing semiconductor crystals



Jan. 2, 1962 F. M. LEOPOLD 3,015,592

METHOD OF GROWING SEMICONDUCTOR CRYSTALS Filed June 11, 1959 INVENTORAGE United States Patent 3,015,592 METHOD OF GROWING SEMICONDUCTORCRYSTALS Frans Martinus Leopold, Eindhoven, Netherlands, assignor toNorth American Philips Company, Inc., New

York, N.Y., a corporation of Delaware Filed June 11, 1959, Ser. No.819,766 Claims priority, application Netherlands July 11, 1958 3 Claims.(Cl. 1481.6) e

The present invention relates to methods of making bodies, moreparticularly monocrystalline bodies, from semi-conductive material bydrawing them upwards from a melt. Such a method has been described byCzochralsky in Zeitschrift fiir Physikalische Chemie, 92 (1917), pages219 to 221.

It is known that, for obtaining rod-shaped bodies of regular shape, itis advantageous to rotate them about their longitudinal axis in drawingthem upwards. Furthermore, it is known that the number of dislocationsin the crystals produced is smaller as the liquid-solid interfaceapproaches to a plane at right angles to said longi tudinal axis. Inorder to obtain such an interface special forms of heating elements havebeen proposed, while it has also been suggested to surround theliquid-solid interface by heat radiators and/ or reflectors.

The present invention has inter alia for its object to permit suchbodies to be made with very few dislocations, and this more particularlyby preventing as much as possible the occurrence of marginal eifects.

According to the invention, such bodies are drawn upwards from a meltwhile being surrounded by a tubular member consisting of the samematerial and being also immersed in the melt.

Viewed in a vertical direction or axial direction, the temperaturedistribution inside the tubular body will be approximately the same asthat in the body surrounded by it. This applies in particulate the innerfaces and outer faces adjacent each other. This uniformity will be amaximum if the tubular body is drawn upwards simultaneously but, unlessimposing the highest requirements, it is alternatively possible for thisbody to be stationary or even to make it melt slowly.

It is known per se that such tubular bodies can be made in a simplemanner by drawing them upwards, namely by immersing a tubular seed ofthe relevant material in the melt and by subsequently letting it grow inthe same manner as was usual for solid rod-shaped bodies.

The material of the tubular member having more lattice defects than thatof the rod-shaped body, may be employed for uses imposing less stringentrequirements or it may be melted up and Worked up again.

In order that the invention may be readily carried into effect, anexample will now be described in detail with reference to theaccompanying drawing, which shows schematically in a simplified manner adevice for carrying out the invention and in which this device comprisesa round crucible 1 in which provision is made of a partition 2 which isspaced from the outer wall, between which walls an annular space 3 isformed. In this space, the semiconductive material, for examplegermanium, is melted, subsequently to which a semi-conductive, tubularmember 4 is drawn upwards therefrom. For this pur- Patented Jan. 2, 1952ICC ' sible and the process is controlled so that the inside diameter ofthe tube 4 and the outside diameter of the rod 6 approach to each otheras much as possible. The partition 2 should only slightly overtop thesurface of the melt. The partition 2 prevents the tubular member 4 fromgrowing in the direction of its axis and uniting with the rod 6.

By now making provision that any part of the rod 6 is located opposite apart of the inner wall of the tube 4, cooling will be low in a radialdirection. This cooling will mainly occur in an axial direction, whichresults in the interface between the melt and the solidified mass beingas planar as possible.

The level of the melt can be maintained constant by replenishmentthrough an aperture in the wall. It may then be desirable locally tointerrupt the partition 2, for example by providing one or more slots 7in order that the level may remain the same at both sides.Alternatively, the spaces at both sides of the wall 2 may be filled upeach separately, while the material in the space 5 may be purer thanthat in the space 3. In this connection, the prescription that thebodies 4 and 6 should consist of the same material is not to beunderstood to mean that there should be no difference in purity or incontent of donors or acceptors, provided that their melting points andheat conductivity do not differ noticeably due .to such difierences.

What is claimed is:

1. A method of growing high-quality semiconductor crystals, comprisingthe steps of providing a melt of semiconductor material, drawing a firstgrowing tubular crystal upwards from the melt, and, simultaneously withthe last step, drawing a second growing single crystal upwards from themelt within the first crystal and separate from the latter and such thatit never extends beyond the first crystal.

2. A method of growing high-quality semiconductor crystals, comprisingthe steps of providing a melt of semiconductor material, drawing agrowing holiow cylindrical crystal upwards from the melt, and,simultaneously with the last step, drawing a growing crystal upwardsfrom the melt and within the hollow cylindrical crystal.

3. A method as set forth in claim 2, wherein the growing conditions arecontrolled such that the outer surface of the inner crystal is close tothe inner surface of the hollow crystal.

References Cited in the file ofv this patent UNITED STATES PATENTS2,730,470 Shockley Jan. 10, 1956 2,822,308 Hall Feb. 4, 1958 2,841,559Rosi July 1, 1958 2,879,189 Shockley Mar. 24, 1959 FOREIGN PATENTS962,553 Germany Apr. 25, 1957

1. A METHOD OF GROWING HIGH-EQUALITY SEMICONDUCTOR CRYSTALS, COMPRISING THE STEPS OF PROVIDING A MELT OF SEMICONDUCTER MATERIAL, DRAWING A FIRST GROWING TUBULAR CRYSTAL UPWARDS FROM THE MELT, AND, SIMULTANEOUSLY WITH THE LAST STEP, DRAWING A SECOND GROWING SINGLE CRYSTAL UPWARDS FROM THE MELT WITHIN THE FIRST CRYSTAL AND SEPARATE FROM THE LATTER AND SUCH THAT IT NEVER EXTENDS BEYOND THE FIRST CRYSTAL. 